1. Field of the Invention
The invention relates to a wafer clamping device which can be used in a plasma reaction chamber as well as a method of clamping wafers.
2. Description of Related Art
Ring clamps for clamping wafers against electrodes in plasma etching chambers are disclosed in U.S. Pat. Nos. 4,615,755 and 5,013,400, the disclosures of which are hereby incorporated by reference.
FIG. 1 shows a cross section of a conventional wafer clamping device in a plasma reaction chamber wherein a wafer clamp 1 presses an outer periphery of a wafer 2 against an electrode 3. An annular barrier 3a surrounds electrode 3 and clamp 1 includes conical surface 1a which mates with a conical surface on barrier 3a. Clamp 1 also includes annular surface 1b extending radially outward from conical surface 1a. During processing (e.g. etching, coating, etc.) of wafers in the chamber, by-products of the process result in a build-up of a deposit 4 (such as a polymer build-up during etching of the wafer) on an edge of the clamp 1 in contact with the wafer 2. The deposits 4 must be removed periodically in order to prevent particle contamination of the wafers. That is, due to rubbing contact between a clamping surface 5 of the clamp 1 and an upper surface 6 of the wafer 2 during wafer transfer, particles of the deposit 4 break off and fall onto the surface 6 of the wafer being processed. Accordingly, it is necessary to frequently shut down the plasma reaction chamber and clean the wafer clamping apparatus in order to avoid the particle contamination problem.
There is a need in the art for a wafer clamping apparatus which does not suffer from the disadvantages described above of the conventional wafer clamping device. That is, a damping member which allows the plasma reaction chamber to run a significantly longer time before cleaning of the clamp becomes necessary would provide higher quality wafers due to reduced particle contamination and would provide economic benefits in allowing more efficient use of the equipment due to reduced down time for chamber/clamping member cleaning.